This invention relates to improvements in syringes and in particular to a syringe having a safety sheath for preventing needlesticks.
Hypodermic needles, for example those used for injections or for taking blood samples, are usually equipped with a removeable cap that protects and helps keep the needle sterile. The cap is usually replaceable to cover the used, contaminated needle and prevent accidental needlesticks. However, accidental needlesticks during recapping have long been a problem. Because of tension, time pressure, or fatigue, needlesticks during recapping occur with alarming frequency despite frequent warnings to be careful, and they account for the majority of accidental needlesticks. Eliminating recapping will not solve the problem because the uncapped needle is so dangerous. Indeed, a large number of accidental needlesticks are caused by uncapped needles found in beds, on floors, or in garbage cans. Even where there is a no recapping policy, the needles are often recapped because of these dangers.
Accidental needlesticks are serious because they can spread diseases, including hepatitis, venereal diseases, and of most recent concern: AIDS. A needlestick causes fear and anxiety in the victim. Both the victim and the patient may be subjected to a battery of expensive, time-consuming tests. Accidental needlesticks during recapping can cost even a relatively small health care institution thousands of dollars annually. Even worse than the economic cost, however, is the transmission of disease.
For example, the victim of a needlestick from a needle contaminated by an AIDS patient must be repetitively tested for several months after the accident. It is documented that after such a needlestick, the victim may test positive for exposure to the AIDS virus, even if the disease is not contracted. A positive test would cause great fear and anxiety in the victim, would seriously disrupt the victim's personal life, and might even end the victim's ability to work in health care.
Despite the very serious nature of the problem, and the severity of the consequences, the problem of accidental needlesticks has persisted for many years without any satisfactory solution. One approach to a solution is to modify the cap. For example, a recent article Sumner, "Needlecaps to Prevent Needlestick Injuries", INFECTION CONTROL (1985) Vol. 6, No. 12, p. 495, discusses the needlestick problem and discloses a needlecap with a small, wide angle funnel surrounding the cap opening. This funnel acts as both a guide and a shield. However, improvements to the cap do not totally eliminate the possibility of needlesticks. The action of bringing the cap and needle together still poses the threat of an accidental needlestick.
Another approach to a solution is to provide a sheath that can be slid down over the needle from behind, eliminating the risky action of bringing the cap and needle together. There have been several syringe constructions having sheaths that can be slid down over the needle. Bastien, U.S. Pat. No. 2,571,653 discloses a Syringe having a sheath slideably mounted over the barrel to hide the needle from view. The sheath has a V-shaped latch that can engage grooves in the barrel of the syringe. This is not a safety device, but merely a device to hide the needle from the patient; the sheath is designed to be freely moveable to expose the needle. Wulff, U.S. Pat. No. 3,780,734 discloses a Hypodermic Syringe Holder and Injector Device having a slideably mounted guard. This is not a syringe but a syringe holder, and is designed for veterinary use. The device would be cumbersome to use and difficult and expensive to make. When the used syringe is removed from the device, the needle will be exposed. Leeson et al., U.S. Pat. No. 3,890,971 discloses a Safety Syringe having a lockable plunger and a lockable, slideable needle cap. The device is very complex and would be difficult and expensive to make. Sampson et al., U.S. Pat. No. 4,425,120, discloses a Shielded Hypodermic Syringe having a needle guard mounted on the syringe barrel for movement between an extended position shielding the needle and a retracted position. The guard is lockable in each position with tracks on the inside of the guard and track engaging members on the barrel. This device would be difficult to operate because the tracks must be aligned with the track engaging members, and it requires a twisting motion to lock and unlock the needle guard. The device would also be difficult and expensive to make.
The inventors have developed a syringe with a safety sheath that eliminates the need for recapping the syringe after use. The sheath is slideably mounted over the barrel of the syringe and after use is simply slid downwardly to its extended position over the needle until it locks, thereby shielding the needle. The syringe has at least one knob projecting outwardly from the barrel. The sheath also has at least one longitudinal slot for receiving the knob. The slot has a first set of opposing tabs projecting into the slot, the lower faces of which engage the top of the knob to retain the sheath in its retracted position. The lower faces of the first set of tabs are angled. These angled lower faces force the tabs apart to clear the knob when the sheath is forced downwardly against the knob. The slot also has a second set of opposing tabs projecting into the slot above the first set. The second set of tabs have angled lower faces and flat upper faces that form a shoulder. The angled lower faces force the tabs apart to clear the knob when the sheath is forced downwardly against the knob. The tabs resiliently snap back after clearing the knob, and the shoulders formed by the upper faces of the tabs engage the bottom surface of the knob and lock the sheath in the extended position.
The syringe of the present invention has a safety sheath that is retained in its retracted position until positive force is applied to overcome the resistance of the first set of tabs. The sheath is easily operated to its extended position by simply pushing the sheath downward. The sheath is easily locked in its extended position by simply pushing the sheath all the way down until the second set of tabs engage the knob. This positive locking action requires no special alignment or manipulation. The locking is positive and easy to visually confirm.
The syringe of the present invention is of simple construction and will be easy and inexpensive to make and simple to use. The locking action is positive and visually confirmable, and without any special manipulation that can be improperly done. The syringe can thus be widely used to eliminate the dangers of needlesticks during recapping.